One band of the RF spectrum which is being increasingly used for wireless communications is the unlicensed Industrial Scientific & Medical (ISM) band at 2.4 GHz. Currently, two types of wireless technology operate in this part of the spectrum.
Firstly, there is Wireless Local Area Network (WLAN) technology which is standardized under IEEE 802.11. One variant of IEEE 802.11 uses a frequency-hopping spread spectrum (FHSS) technique with 1 MHz channel separation and pseudorandom hops across 79 channels. Another variant (IEEE 802.11b) uses direct sequence spread spectrum (DSSS) techniques, with 22 MHz channels. WLAN technology is widely used in offices, homes and public places to support networking between users.
Secondly, there is Wireless Personal Area Network (WPAN) technology, which is standardized in IEEE 802.15.1. This is a 1 Mbit/s FHSS system which uses the same 79, 1 MHz-wide channels that are used by the FHSS version of IEEE 802.11. IEEE 802.15.1 hops pseudorandomly at a nominal rate of 1600 hops/second. IEEE 802.15.1 is intended as a low power, short range (<3 m) technology for interconnecting devices such as mobile phones, portable computers and wireless handsfree headsets with fixed devices or other portable devices. One commercial implementation of IEEE 802.15.1 is known as ‘Bluetooth™’.
Since both IEEE 802.11 and IEEE 802.15.1 operate in the same 2.4 GHz unlicensed frequency band, there is mutual interference between the two wireless systems which may result in severe performance degradation. The interference is of most concern with IEEE 802.11b as this uses a static channel (i.e. no frequency hopping). Factors which determine the level of interference include the separation between the WLAN and WPAN devices, the amount of data traffic flowing over each of the two wireless networks, the power levels of the various devices, and the data rate of the WLAN. Also, different types of information being sent over the wireless networks have different levels of sensitivity to the interference. For example, a voice link may be more sensitive to interference than a data link being used to transfer a data file.
The IEEE has produced a Draft Recommended Practice IEEE P802.15.2/Dec. 20, 2002; “Telecommunications and Information exchange between systems—Local and metropolitan area networks Specific Requirements—Part 15.2: Coexistence of Wireless Personal Area Networks with Other Wireless Devices Operating in Unlicensed Frequency Bands.” This document outlines the interference problem and provides some guidance for how WLAN and WPAN equipment can coexist. Two categories of coexistence mechanisms are proposed: collaborative and non-collaborative. Collaborative coexistence mechanisms exchange information between two wireless networks. FIG. 1 shows an example piece of equipment 100 which includes a WPAN transceiver TX1 and a WLAN transceiver TX2. Equipment 100 can be, for example, a portable computer with the WLAN supporting a connection 40 with a WLAN base station 45 and the WPAN supporting a connection 30 with a WPAN device which, in this example, is a wireless headset 35. Some of the possible sources of interference are shown: WLAN transmissions from BS 45 may interfere with reception of WPAN traffic at TX1, or WPAN transmissions from TX1 may interfere with WLAN reception at the base station 45 (path 32 ); WPAN transmissions from head set 35 may interfere with reception of WLAN traffic at TX2, or WLAN transmissions from TX2 may interfere with WPAN reception at the head set 35 (path 42 ).
One solution proposed by the IEEE Draft Recommended Practice Document is to provide a packet traffic arbitration (PTA) control entity which communicates with both the WLAN station and WPAN station and provides per-packet authorization of all transmissions. FIG. 2 shows an apparatus 100 with an arbitration device 130. Both transceivers TX1, TX2 must request permission to transmit or receive and, in response, the arbitration device 130 will either grant or deny the permission to access the shared spectrum to transmit or receive a data packet. The recommended interface between a WPAN transceiver and an arbitration unit is shown in FIG. 2 as lines 151-154.    The Bluetooth device and the WLAN may not be placed really close to each other (maybe 10 cm distance) in this case increasing the number of the pin in the coexistence interface increase the complexity of routing them in the board and most likely it increases the board size.    The pin count of both chips will increase and this is a problem especially for the Bluetooth which is a very small chip and there is very little room for adding pins.
The WPAN can support multiple simultaneous links, which can be voice, data or control information. One of the lines between the WPAN transceiver and arbitration device 130 is a status line 152 which can be used to indicate the priority level of the link. The priority can take the value ‘1’ or ‘0’. The arbitration device uses the priority level to decide whether the WPAN should be granted access to the shared RF band. Links with a priority ‘1’ can be granted access to the band in preference to the WLAN, while the links with priority ‘0’ are not. One problem with this arrangement is that, during a long period of WLAN activity, such as a file transfer, the WPAN links with priority ‘0’ will be refused. The Bluetooth protocol requires transceivers to make one TX/RX operation within a predetermined timeout period to maintain synchronization. In an environment where the Bluetooth device shares the RF band with a WLAN, this can be difficult.